Abstract
Abstract. Dispersal and grouping patterns form the foundations of social interactions in group-living mammals and are the outcomes of a complex interplay between inbreeding avoidance, kin cooperation and competition, predation pressure and food resource distribution. In species where both sexes disperse, the potential for kin-biased associations would seem limited. In one such species, the western lowland gorilla (WLG), short-term data suggest that female kin associations may be present due to directed local dispersal decisions, but monitoring of groups over longer timescales is needed to better elucidate this pattern. Using autosomal genotyping of 419 faecal samples representing 85 unhabituated gorillas collected non-invasively over 5 years in a 132 km2 section of Loango National Park, Gabon, we investigated the dynamics of WLG group composition, social structure and patterns of dispersal. By revealing two group dissolutions, one group formation and the movement of 13 gorillas between groups, this study demonstrates the utility of genetic analysis as a way to track individuals, groups and population dynamics on a larger scale than when monitoring the behaviour of a limited number of habituated groups or through one-time genetic sampling. Furthermore, we find that females are found in groups containing their female kin more often than expected by chance, suggesting that dispersal may not impede female kin associations in WLGs.
Highlights
Group living in many mammal species is generally explained as an arrangement that maximizes the potential benefits of kin cooperation and predator avoidance (Clutton-Brock and Lukas, 2012; Handley and Perrin, 2007)
Unlike most mammal species which display predominantly male dispersal (Greenwood, 1980), great apes such as eastern gorillas, western lowland gorillas (WLGs, Gorilla gorilla gorilla), bonobos and chimpanzees typically exhibit dispersal of females from the natal group at maturity (Greenwood, 1980; Pusey and Packer, 1987; Robbins, 2010; Wrangham, 1979), and these females may disperse to other social units multiple times in their lives (Boesch, 2009; Stokes et al, 2003)
We identified a total of 85 different gorillas during 2005–2009 in a 132 km2 area of Loango from three different groups and two females of unknown origin
Summary
Group living in many mammal species is generally explained as an arrangement that maximizes the potential benefits of kin cooperation and predator avoidance (Clutton-Brock and Lukas, 2012; Handley and Perrin, 2007). WLG males consistently disperse from their natal group and become solitary or reside in non-reproductive social units before possibly acquiring females and forming their own reproductive groups. These reproductive groups nearly always contain only a single fully mature adult (silverback) male along with mature females and immatures of both sexes (Bradley et al, 2004; Gatti et al, 2004; Robbins et al, 2004). New groups may form when females join lone silverback males or females transfer to existing groups dur-
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